1. archPbMoO4 scintillating bolometers as detectors to search for neutrinoless double beta decay of 100Mo
Serge Nagorny
INFN – Gran Sasso Science Institute, L`Aquila, Italy
on behalf of the CUPID-0 collaboration
1st March 2017

2. Double Beta Decay (DBD)

3. DBD active nuclei in the nature

4. Which nuclide is the best for such search?
from experimental point of view
Environmental gamma background of 238U and 232Th chains
2615 keV
48Ca
82Se
96Zr
100Mo
116Cd
150Nd
76Ge
130Te

5. Development of TeO2 bolometers
TeO2 is wide used acousto-optic material with market of tens MEuro/year and well-developed technology of production

6. CUORE Upgrade with Particle Identification
a future ton-scale bolometric neutrinoless double beta decay experiment with improved sensitivity, based on the experience and expertise learned in CUORE
The CUPID goal is the use of the unique CUORE LNGS, once CUORE completes operation, as well as using of upgraded detector technology in order to reach higher experimental sensitivity
New detector technologies (background rejection or surface events ID)
Isotopic enrichment
New purification and crystallization procedures
Stricter materials selection

7. Czochralski

8. Working principle of scintillating bolometers

9. CUPID-0 Demonstrator array of enriched Zn82Se scintillating bolometers
Total enriched 82Se isotope mass is 7 kg
Expect background < 10-3 c/(keVkgy)

10. Some crucial detector parameters
Radiopurity (internal background)
Light Yield
FWHM
PSD
High content of isotope of interest
Well-developed technology of crystals production

11. CaMoO4 2003, Korea 2005, Ukraine 2004, Moscow 2007, Moscow
2015, Novosibirsk

12. ZnMoO4
2008, Moscow
2009, Kharkov
2012, Kharkov
2012, Novosibirsk

13. Li2MoO4
2004, Moscow
2014, Kharkov
2015, Novosibirsk

14. Mo-containing crystals
CaMoO4
ZnMoO4
Li2MoO4 ……
No other applications
No other applications
No other applications
What about PbMoO4?
PbMoO4 crystal is one of the most efficient materials used for acousto-optic devices (modulators, deflectors and phase-shifters) which possess a low optical losses, high optical homogeneity, high stability to laser radiation
The same like in case of the TeO2 crystals!!!
Market demands & developed technology

15. archPbMoO4: conventional Czochralski technique
archPbMoO4 boule
Total mass is 175 g
20×90 mm
Highly purified archaeological lead, > %
Re-crystallized MoO3 powder, > 99.99%
Conventional Czochralski technique
Production yield is about of 50%
Light detector
archPbMoO4
57 g
20×25 mm
Low-background measurements
LNGS

16. archPbMoO4: Light Yield @ low temperature
 10 times

17. archPbMoO4: Light-vs-Heat scatter plot
 + 
 +   
Well separated population of different type of events

18. archPbMoO4: pusle-shape discrimination
Shape parameter, a.u.
Energy, MeV
alphas
beta/gammas

19. archPbMoO4: alpha spectrum
Excellent energy resolution!
FWHM = keV (226Ra)
FWHM = keV (40K)

20. archPbMoO4: internal alpha contamination
Chain
Nuclide
Activity, mBq/kg
232Th
10±7
228Th
99±9
224Ra
86±8
220Rn
21±5
212Bi
49±7
238U
38±6
234U
98±9
230Th
13±3
226Ra
2310±42
222Rn
2370±42
218Po
2340±42
210Po
266±16
235U
14±3
227Th
17±4
223Ra
30±5
219Rn
5±2
211Bi
HUGE!!!
…but we have explanation
based on our experience
with ZnSe crystal

21. Separation process of ZnSe sample (15/01/2013)
Piece of ceramic
m = g
226Ra & daugthers (about 0.2 kBq/kg)
40K nuclide (1 kBq/kg)
High contamination observed in archPbMoO4 crystal is caused by incident during the growth process, when a small piece of ceramic ( g) fall dawn to the melt, but NOT by the properties of the material itself

22. 2222
Pt-crucible
conventional Czochralski
LTG Czochralski

23. PbMoO4: at Novosibirsk
Presently used natural Mo & Pb
No problems in crystals growth
Yellow color is due to the low purity of initial materials
First trial with archaeological lead will start this week!

24. New batch of archaeological Lead @ LNGS
Reduction
of impurities level
in more than 10 times
Yield  95%
After purification by double stage
vacuum distillation
Sn = 5.2 ppm
Sb = 2.6 ppm
others on tens ppb level

25. Some useful parameters
Li2MoO4
ZnMoO4
PbMoO4
CaMoO4
LY, keV/MeV
0.13
0.26
1.2
0.71.4
LY, keV/MeV
0.43
1.54
5.5
3.56.8
FWHM, keV
@2.6 MeV 5
6.8
< 5 9
PSD
yes
Particle identification
 (Mo), % 55 43 26 48
N(Mo)1023
in 1 cm3
0.105
0.115
0.112
0.131
Background level
low
low ???
high
Hygroscopicity no

26. archPbMoO4: SUMMARY
archPbMoO4 crystal produced from the archaeological lead demonstrates excellent performance as a scintillating bolometer
Crystal’s radiopurity soon will be re-checked with new crystals produced by LTG Czochralski method
archPbMoO4 crystals is promising material for a future ton-scale bolometric DBD experiment with improved sensitivity

28. … just visiting a friend in Sicily
06/09/2016
…it is about of kg of Roman lead!

29. …or we can go deep underwater to discover a sunken ships and to excavate the Roman lead
with C-Explorer 3 submarine…

31. From the crystal producer viewpoint
Well-developed technology of detector production means:
Developed technology of purification of initials reagents
Developed technology of large volume crystal production
Possibility to fast scalability of growth process
High yield of good crystals
Developed technology of recovery of the rest materials after the growth
Easy handling/machining
Other applications of this compound, or market demands exactly on such large single crystals
NO RISCKS for investments in such R&D or production,
and expected profit in the future